\_l_/ -- That is about how the bolt looks. The edges of the battery clamp are straight for the most part.
So when the bolt is tightened the fingers of the clamp are forced together.
Being it is lead and soft, if it's overtightened or through repetitive use, the clamp will deform and the bolt can not clam tight enough.

The proper fix is going to be a new clamp or cable assembly.
A quick/temporary fix may be to simply 'shim' the bolt. Maybe a thin piece of metal on either side of the bolt will help.